It is conventional to incorporate fine grain silver halide particles, commonly known as Lippmann emulsion, in an image element to scavenge process seasoning fragments. The level of Lippmann emulsion can effect the photographic elements overall sensitometric properties such as contrast and interimage. As for the conventional arts, a "Lippmann" emulsion, having a grain size of 0.050 .mu.m, is disclosed as a silver bromide fine grain emulsion, e.g., in T. H. James, The Theory of the Photographic Process, 4th Ed. Lippmann emulsions typically have an average size between about 0.030 and about 0.10 .mu.m. Methods for incorporating fine grain silver bromide and Lippmann emulsion into a photographic element have been described in U.S. Pat. Nos. 3,661,592; 3,704,130; 5,196,300 and 5,523,200.
It is also well known in the photographic art to incorporate photographically useful compounds, for example, ultraviolet ray absorbers, which are dispersed in an aqueous medium containing a hydrophilic colloid, such as gelatin. The ultraviolet absorber compound may be a liquid which may be directly dispersed into the aqueous medium or it may be a solid or liquid predissolved in an organic solvent. Typically, the photgraphically useful compound is dissolved in a permanent organic solvent or in combination with an auxiliary organic solvent which is later removed by evaporation, washing or dialysis. The photographically useful compound or solution thereof is mixed with the aqueous medium, which may optionally contain a surfactant, under conditions of high shear or turbulence to break the organic phase into submicronic particles. Different methods for incorporating an ultraviolet ray absorber into a photographic element have been disclosed in U.S. Pat. Nos. 2,739,888; 3,215,530; 3,352,681; and 3,707,375.
Another method of incorporating an ultraviolet ray absorber into a photographic element is by loading such an absorber into pre-formed latex particles as described in U.S. Pat. Nos. 4,199,363; 4,304,769; 4,247,627; and 4,368,258. In this process, a hydrophobe, such as an ultraviolet ray absorber, is first dissolved in a water miscible organic solvent and then blended with an aqueous latex. Alternatively, U.S. Pat. No 5,536,628 describes a process for incorporating absorbers into a pre-formed latex polymer particle. In the process a polymer latex of known solids is heated with stirring to 70 to 80.degree. C. The absorbing compound is heated until it reaches its liquid state and is mixed with the polymer latex at high shear to generate an emulsion. The emulsion is then passed through a high energy homogenizer at least once to form an absorber impregnated latex polymer dispersion.
The resulting ultraviolet absorber dispersion can be coated onto a support or incorporated into a silver halide emulsion or other photographic composition which is then coated onto a support. It is well known to incorporate photographic dispersions of ultraviolet absorber compounds into a composition containing Lippmann emulsion. Such a composition is commonly referred to as a melt and can also contain other components such as, acids or bases to control pH, coating surfactants, thickeners, salt solutions; and the like. During or just prior to the coating step, the melt may be heated to about 45.degree. C. and maintained at that temperature for up to 24 hours. It has been noted that in certain instances the dispersion particles containing the ultraviolet absorber compounds undergo an undesirable increase in particle size when Lippmann emulsion is present in the coating composition. If the particle growth is severe enough, extremely large particles (greater than 3 .mu.m in diameter) can be formed. Particles in this size range are undesirable in manufacturing since they can lead to filter plugging during coating operations. These particles may be visible in magnified prints or projections representing a physical defect in the coated photographic product. In addition, the large droplets may reach sizes which are larger than the thickness of the coated layer and may degrade the mechanical properties of the layer such as scratch resistance, pressure sensitivity, adhesion; and the like.
An attempt to slow the particle growth in photographic dispersions is disclosed in U.S. Pat. No. 5,468,604 to Zengerle et al. Zengerle et al. disclose a method for stabilizing a photographic dispersion by addition to the dispersed phase of a hydrophobic, photographically inert compound which has a logP.sub.(cake) greater than 9 and does not solidify or gel the dispersed phase. While this method does slow particle growth in the photographic dispersion, it does not eliminate the formation of large droplets in coating compositions containing photographic dispersions of ultraviolet absorbers and fine grain silver halide particles.
Therefore, the problem solved by the present invention is to inhibit large particle formation in a photographic dispersion during the presence of a fine grain silver halide particle in the manufacturing process of an image element.